Writing instrument



March 16, 1954 H, R, FEHUNG' 2,672,127

WRITING INSTRUMENT Filed July 12, 1949 2 sheets-Sheet 1 A ltorneys 2 i 6 d F a 5. 3 7 Il 5 AW [1V L \\.\\v\\ .4 H 3 N M3 March 16, 1954 H. R. FEHLING WRITING INSTRUMENT 2 Sheets-Sheet 2 Filed July l2, 1949 Attorneys r Patented Mar. 16, 1954 WRITING 1N STRUMENT vHans Reinhard `Feh'ling, London, England, as-

signor to Uompania str'ial S. A., Mont Uruguaya de Fomento evideo, Uruguay Application `July 12, 1.949, Serial Nn. 104,242

Claims priority, application 'Great Britain "July 15, 1948 This :invention is concerned `Witl'l 1an :improved reservoir specically :intended for-reseryoir Writing instruments of theball tip type wherein 'the :writing extremity comprises a writing :ball frotatably housed in and partly protruding 'from -a `sockel; or housing, which ball :is ysupplied with :ink ,from a reservoir -zby means of at ,least rone rfeed duct or passage Y.which communicates with the base of the socket or housing so that, 1as the ball is Arotated .being :moved over :in .contact with a surface `such .'-for example as that nf a sheet l,olf vpaper, ia thin 4ilm of is camiecl by Athe ball through the narrow gap between 'it and its housing v:and is deposited as a trace @on thesaid surface. In ,general :satisfactory writing instruments of this 'type'iaave been manufactured and .have 'been equipped withta vented reservoir in the form of a small bore tube.

`Practicai considerations in a writing instrnment place an upper limit on the .capacity .of I

.such a reservoir. whereas it Ais desirable ato provide an instrument of the type rspecied va reservoir of .appreciable capacity. One .problem 'that is encountered this provision Ya large capacity reservoir ris that of preventing the ingress of fair, avoiding leakage-'of ink, and avoidlingan air lock caus'ng :the cessation ink now) yas the ink is grad-uarly usednn rtn'writing.. Theoretically it is :possible to mercome 'mese cliculfties lay :employing an inl: reservoir f'tvlsaich resembles an .open-ended cylinder `and placing nnen the ink sa :pistondike float, ft'hs `float .being :such :a ft within `the cylinder that :on the one ,band vit prevents the ingresszo air the .leakage nf ink, while onfthe other hand is canabe :mor/- ing down the cytnder ns the ink is used The commercial manufacture nf .such a mservoir .on a repetition basis, however, presents diiculties. Specidca'lly, it is dilncnlt to ensure that the r-oat has the correct buoyancy and that ithe :gap ibe tween its peripheral surface and the interior surface ef :the reservoir is of the correct dimension. Considering in tne first place conditions obtain ing when the writing instrument is the writingy attitude, viz. with the float uppermost, it will be appreciated that the float will be immersed 'in the ink to a greater nr lesser rextent according to its buoyancy. It will also 'be appreciated that strcngfcapillary forces will beset `upinftlne narrow radial gap "between fthe exterior peripheoal sur face of the oat and the interior .surface of surrounding walls of the reservoir. These capii "1a-ry lforoes will :cause the ink .to rise within the gap @to a height :greater that to which they would lrise merely by Vvirtue #of fdisnkioenient nf .ink bythexfioat; `the ink in :the gap nee'essarfii-y terminates in -a meniscus. The location ,of this men-scus will therefore lbe affected by several yfactors including the :buoyancy fof the float and the width of the gap (the narrower the nap the stronger thecapl-lary forces and the nig-her the location of the ',meniscus), Indeed conditions may be such that the menisous, .instead of losing located within the gap below or at the top end of :the neat, may extend from the top fend sur-- face of the float to fa ,higher level on the anser* voir walls. lf this happens there ,is the danger of ink seepage, particularly .if there is an vnlm on the reservoirwalls and fthe formation ozf such 'an ink in :inevitable fas the reservoir is gradually emptied. However; the la'nstrument spends only a part of its life fin :the writing atti tnde, for when not :in :use it :is commonly carried iafll uppermost.. In this attitude, `if Ithe ioat .is buoyant it tends ftc ,rise :in y,the ink with a com sequent risk of seepage past :the neat. It will therefore be appreciated that accuracy in manu- `facture fmnst tbe of a very fhghdegree and it :has `been found V*that `an error fof .1% in the weight tof the float `may :under certain circumstances produce seepage :in one or other attitude ,of :the instrument.

A specific object of the present invention :is 'to prov-ide an improvedrinstrument of the type speci ned, in which the above mentioned diinculties are nbviated .or minimised.

"Slfth this and other objects in View Ythe in vention provides -a reservoir 4writing instrument nf the type specified 'liaving a reservoir ...of tubo lar internal Vform with :a cross sectional .area of not more Vthan lo Aand not vless than 5 sq. anni., charged with a suitable and containing a reservoir sealing member which is a sliding nt :in 4the reservoir and Vrnnrnalli,I moves :along the reservoir :in 'contact -With the ink as the latter is used up in writing, characterised in that the :reservoir further incorporates means for compensating any tendency of the sealing .manchen in any attitude oT the instrument, to mon/ement towards the ball other than the :aforesaid normal movement land any tendency .of "the sealing `member to ,movement away fnom .the ball when the instrument is invented. The prorision of this means 'permits of Vwide manufacturing tolerances, as regards :size .and Weight, *in the seating member without encountering undue 4risk that when the instrument .is in the `writing attitude the sealing member will .descend towards the lball :and lthe risk that when the dnstrnmen-t iis inthe `irl-sacrified nttttmie the sealing wil-1 drop out of the ink. It is preferred that the reservoir shall be of circular or other cross section with a smooth interior. t is necessary to avoid the use of a reservoir of angular cross section or any reservoir having sharp corners as in a square in order to avoid the phenomenon known as capillary creep and for this reason if the section of the reservoir example of corrugated formation it should not have any curves forming a radius of less than 1 mm. i

A suitable ink is one which is suitable for use in a Writing instrument of the type specied, primarily in that it gives an even trace and does not result in the ball seizing or getting clogged up or gummed up, and in that its viscosity is not so high as to prevent an adequate ink feed to the ball when the instrument is being used. The present state of knowledge indicates that a suitable ink must be oleaginous containing a dye stuff which gives the required colour or shade, its viscosity preferably being not less than 15 poises at all temperatures likely to be attained by the instrument in normal use (e. g. not less than 15 poises at 37 C.).

Speciiically the aforesaid means may be a balancing member which is located in the ink space beneath the sealing member and is free to move therein towards and away from the sealing member under the influence of gravity as the attitude of the instrument is changed,

The invention further provides a reservoir suit-- able for a reservoir writing instrument o the type specified which is of tubular internal form with an internal cross sectional area of not more than 40 and not less than 5 sq. and contains a reservoir sealing member which is a sliding iit in it at the end of the ink space remote from the ball and a balancing member which is free to move in the ink space and has a bulk density diiering from that 'of the sealing member, the construction and disposition of the parts being such that when the reservoir is charged with a suitable ink of a density intermediate the bulk densities of the sealing and balancing members, a meniscus is formed between the sealing member and the inner surface of the reservoir and the sealing member is maintained in stable equilibrium at that end of the ink column remote from the of the instrument. The bulk density of the sealing member or balancing member is ascertained by dividing the weight of that member (in air) by the over-all volume of the member (including the volume of ani,7 cavity therein which is not i lled with ink) thus for example a bulk densitv of 1 gr./ cc. would indicate that the member would just neat in water.

While the sealing member mav have a bulk density which is greater than that of the balf ancing member it is preferred that this bulk density shall be less than that of the balancing member.

It has been ascertained that commercially satisfactory results are obtained if the radial clearance between the sealing member and the interior surface of the reservoir is between 0.01 mm. and 0.20 mm. (assuming the clearance to be equal all round the sealing member) but best results are obtained if the clearance is between 0.05 mm. and 0.08 mm.

A further and important feature of the invention resides in the provision at the rear tace of the sealing member of. an annular rim which presents a sharp inner edgelimiting the inw-ard is not circular or oval but is forv ball in all attitudes spread of the meniscus across the rear face of the sealing member. The radial spacing between the said edge and the interior surface o2 the reservoir should preferably be less than 0.65 mm.

The foregoing and other features of the invention are incorporated in the constructions that will now be described with reference to the accompanying drawings in which Figures 1 and 2 illustrate a reservoir writing instrument equipped with a reservoir according to this invention, vwhen in the writing and inverted or carrying attitudes respectively;

Figures 3 and 4 are like views showing a modiiied arrangement of reservoir, while Figures 5 and S are like views showing a urther modification in which the change in buoyancy is effected by means of a gas bubble.

Figure 7 is a longitudinal section through a reservoir writing instrument according to this invention or through a unit which (being complete with reservoir and writing extremity) may be employed as a re-fill in a writing instrument;

Figure 3 is a cross section taken on the line VIII-VH1' in Figure '7;

Figure 9 is a longitudinal section through part of the reservoir and its sealing member, while Figures 10 and 11 are longitudinal views through the rear end of a reservoir illustrating arrangements which may be adopted for the purpose of preventing capillary creep.

In the accompanying drawings Figures 1 to 6 are largely diagrammatic and the writing instrument itself is not shown in any detail for the general construction of instruments of the type specified is now well understood. vThe instrument comprises a reservoir l of cylindrical form attached to a writing extremity 2 incorporating a writing ball 3 rotatably housed -in and partly protruding from a socket or housing, this ball being fed from the reservoir by a small bore feed duct li.

The reservoir i is of substantial capacity and leakage of ink is prevented by a device consisting of two superimposed members 5, The member 5 which is uppermost when the instrument is in the Writing attitude (Figure 1) is the sealing member aforesaid and has a positive buoyancy (i. e. is capable of floating on the surface of a wide expanse of the ink). It is of cylindrical exterior configuration and is a sliding fit in the interior of the reservoir, like a piston. The lowermost member 5 is the balancing member and is heavier than ink so that it tends to sink When submerged in ink. That is to say the sealing member 5 has a bulk density which is less than. and the balancing member f3 has a bulk density which is greater than, that of the ink. When the instrument is in the writing attitude, the member 5 will be relieved of the weight of the member 6 and will therefore float. When the instrument is inverted to the carrying attitude however, in which the member 5 is lowermost, the member descends through the ink until it rests on top of the member 5. Therefore the sealing device coniointly formed by the members 5, G, has no buoyancy i. e. no tendency to rise through the ink.

The member 6 is shown in the form of a hollow cylinder but it will be appreciated that it may be of any shape, so long as its shape is such that it can freely move from one end of the voir to the other and such that when the instrument is in the writing attitude it does not block the feed duct il. The reservoir tube l may essaies 5 be iopensat its rear l.,en`d, bult 4preferallmy it is ,closed by aiplug 'l provided with a vent :hole 8.

'The maority of inks likely to be ius/,ed in bail point ywriting instruments of the type speeiee'. will have a density `of approximately 1 gram/cc. and a surface tension of .about 35 dynes per scm. As a. result of experiments .it has been found that the following values .are satisfactory:

edge :of the piston fskirtfindicated at 9 in Fig. 9

should be quite sharp and the distance between this edge and the interior surface of the .reservoir as `indicated by the :dimension 'Y in Fig. v9, should prererably be less than 1'0.65 mm.

Iii-addition the following condition lshould Valso be speciiied-s weight .of `member .5 in liquid .weight fof member .6 in liquid.

The weight in airis `the normal weight as obtained Aon a balance. The weight in liquid is nless fand takes into account the buoyancy due 'to .the .displacement of -.the vliquid by the member.

The sealing :member :.5 .may be constructed or" any plastic :that is 'not attacked `by and does .not swell in o'leaginous liquids, or any comparatively flight material :such tor example :as :aluminium and its various alloys. A particularly suitable alloy is that which is .sold `under the registered trade-mark Dnraluminr The bulk ldensity y.of the sealing member or piston should not-eXceedOJQ g-r./cc. and .theiollowing are examples of sealing members .or ipistons intended for use in a reservoir :of .5 mm. internal diameter.

Material-that sold y.under the registered .trademark fDuralumin:

The `balancing member employed with the piston `of Example A41 or Ebramp'le 2 ymay consist ei aleadshot having an average vc'l-iameter of 4 and Weight '0.4gr. (bulk density 11.4 gr/cc) or :a .steel ball 'having a nomi-nal diameter of sie" (about 4 mm.) 4and a `weight of 0.*2'6 gr. (bulk density 7.9 gin/cc!) but more than one ball 1may `be employed providing that the Atotal'weiglfi-t vdoes not exceed 0.6 grs.

vSuch a steel ball or lead vshot is indicated at (te int-Eig. 7, but particulars as Ato weight also apply ...to .an annular balancing member of the shape Fi shown yat 6 in Figs. '1 and 2 kwhen made of 'lead .or steel. JIn order to prevent such a lbali yobstructing vthe ink "flow through the 'duct il, the .end wall of `the reservoir may be cut across with a groove 10, Figs. 7 and 8. v

It 'is :not .essential that the lighter one .of the two members shall be uppermost when the instrument is in the writing attitude .and Figures .3 and a illustrate a construction .in which the lighter member is lowermost. `In these figures the balancing member y6a has .a lpositive buoyancy and the .sealing member 5a has a less buoyancy and preferably a .negative buoyancy. In `the writing attitude, Figure vv3., fthe lmember :6a will float on top of the ink and will support Vmember y50i, the conjoint Abuoyancy of these two members therefore being positive. When the device .is inverted to .the writing attitude the member lia (having a positive buoyancy) rises through 'the ink and therefore leaves the `member 5a (having negative buoyancy) at the bottom of the 'ink column.

The balancing member a is .conveniently .constituted by a bubble :of air or other gas enclosed in a very thin walled shell. The .shell may be manufactured 'by a .bubble-blowing technique, employing va film-forming synthetic resin :such for example as polyvinyl alcohol.

it will be noticed that the sealing Amember fia is shown as being of solid construction indicating the use of a material having a density slightly lgreater than that vof the ink. The rear `end .of this sealing member .5a is provided with an annular rim ii the inner :ed-ge *.9 of which is sharp and is spaced from the interior Wall of thereser- Voir as already described with reference to Figs. i andz.

it is `within the scope .of the :invention 4to :employ a bubble of air, or gas which fis:not enclosed in a shell, as indicated at .6b in Figs. 5 and 6. If such an arrangement is adopted the entry to the feed duct i must be `kept comparatively small (for example not `mo-re than 1 mm. in diameter) to prevent the air 'bubble from entering it. Alternatively however, there is provided 'at the entry to the feed duct t a filter or trap which affords llittle resistance tothe passage of ink devoid 0f bubbles so that an adequate supply `of ink by 'the writing ball .3 can be maintained, `but is :capable .of .resisting `:or preventing the passage .of gas bubbles. This 'lter .or trap is vshown as consist- :ing of a porous `plug l2, this :plug .having approximately 56% porsoityand a pore sizeof approxi- .mately .0.1 mm. (50% porosity .means that -the rtotal pore volume of the .material is 5.0% `of the total bulk volume of the material). Fundainentally any porous material in which the pores .are in .cernmunicatian with one another, .in which :the porosity iis `sniciently high, .and in which .the

g' pore .size is suiiieiently large, will be suitable if it is :chemically inert with regard to the ink. Examples zare porous plastics, various sinteied 2maanfi eeen sinte-iedpg'l-ass. .It l be vnoted that in the nib .down position; Y' ig. an :air bubble may hold up a .solid e., that the :downward force of gravity clue to: plug can -bernade lower than the 'npwar torce ci buoyancy due to the air bubble.

it will readily be appreciated from the drawing't-hi s not so to ariange the meme voluineloi" the plug is approximately a. .to of .air bubble. Assuming this ease.. the-.relative ygravi-ty forces are `.evi-

.ia-l te the relative .density :of the two in There is nodifculty in providning with a bulk density a little higher ing a than tha -oi the ink. However, ,if it is assumed 'that the density :of the plug is as high as .1.3 (as in the example given in the description herein), then, with the density ci inlrgat 1.0, the downward force exercised by the plug, per unit volume, is equal to the difference in density, i. e., 1.3-l.0=0.3 gr./cc.

rlhe same applies to the bubble, i. e., its lifting force per unit volume is equal to the difference in the densities between ink and air, which is 1.0-0.0013=approximately 1.0. The buoyancy of the air bubble is, therefore, more than 3 times larger than the weight of the plug in ink. Hence, even if the volume of the air bubble were half of the plug there would still be an excess of buoyancy. It will be noted that the density in ink of the bubble and of the plug is diiferent from the density in air.

Only the most violent shocks would make any impression on a single large bubble floating in our inks. Any air bubble entering the lter would immediately create menisci of Very small curvature in the interstices of the filter. The corresponding capillary forces are such that they could not be overcome by the small gravity force of the ink column in the reservoir. The latter is, however, large enough to force pure-air-free ink through the filter at the required rate against the frictional resistance of the filter.

In other words, the air is not prevented from passing due to its frictional resistance or to the size of the air bubble but entirely due to the capillary resistance which is automatically built up when it tries to enter the interstices of the filter.

The following example is applicable to a construction shown in Figs. 3 and 4 and that shown in Figs. 5 and 6:

Example 3 Internal diameter of reservoir, 6 mm.

Material of sealing member 5a a synthetic resin having a density of about 1.3 gr./cc.

Length of sealing member, not exceeding Diameter of sealing member, 5.85 mm.

Diameter of bubble a or yFb (the bubble being assumed to be spherical) mm.

for the ink to creep out at the rear end of the r reservoir may be minimised by providing the 'vent S in plug 'la which, as shown in Fig. '7, has a conical inner extremity so as to present a sharp edge at the inner end of the vent 8, the capillary creep is preferably prevented by arrangements and as illustrated in Figs. l0 and 11 respectively. According to Fig. 10 the interior of the reservoir near the plug is provided with a plurality of annular grooves I3 presenting sharp edges at the inner surface of the reservoir. Each groove may be V-shaped, having an included angle of 60 and a depth of 0.5 mm. According to Fig. 11 the interior of the reservoir is formed with a series of shoulders l presenting sharp edges, the depth of each shoulder being preferably at least 0.25

The reason why the sharp edges prevent capillary creep along the length of the reservoir is as follows:

` When a liquid lm is creeping along a surface,

the surface tension of that lm resists any tendency to a sudden change in direction because in order for it to move over an edge the film surface has te become strongly curved. Such a curvature can only be produced if the liquid at this point is at a pressure higher than atmospheric pressure. Such a high pressure can only be produced by force of gravity (in which case the liquid must first accumulate) or by shocks or the like. It will therefore be apparent that the sharper the edge the more abrupt must be the change in direction and the smaller the radius of curvature, and therefore the greater reluctance on the part of the film to move over the edge.

It will readily be appreciated that thesek ccnstructicns render the dimensions and weights cf the members 5 and 5a much less critical, for it is quite easy so to arrange matters that permissible size and weight variations are within the range of ordinary goed manufacturing tolerances.

l claim:

i. A writing instrument of the type specified, comprising a ball writing end, a reservoir connected to the writing end, said reservoir being of tubular internal form with a cross sectional area of not more than 40 and not less than 5 sq. mm., said reservoir being adapted to contain ink of a viscosity of not less than 15 poises at 37 C., a reservoir-sealing member in the reservoir forming a sliding iit in the reservoir with the inner wall thereof, said member being adapted to normally move inside said reservoir in contact with the ink as the latter is used up in writing, a balancing member between the ball writing end and the sealing member, said balancing member being movable in the ink in the reservoir and having such a bulk density, that it cooperates with the sealing member, when necessary, to compensate, in any position of the writing instrument, any tendency of the sealing member to move through said ink toward the writing point.

2. Apparatus according to claim 1, wherein the radial clearance between the sealing member and the interior surface of the reservoir is between 0.01 mm. and 0.20 mm. and is preferably between 0.05 mm. and 0.08 mm.

3. An instrument according to claim 1, wherein the said balancing member moves towards and away from the sealing member, under the inuence of gravity as the attitude of the instrument is changed.

e. A reservoir writing instrument of the type specified, having a smooth tubular reservoir of suitable cross-sectional area, containing a continuous column of suitable ink and a sealing member which is a sliding nt in the reservoir and has a bulk density less than that of the ink, and a balancing member which is located in the ink column and has a bulk density greater than that of the ink, the combination being such that, when the instrument has its ball tip downwards the sealing member floats separate from the balancing member in a suitable position at the end of the ink column remote from the ball tip, and when the instrument has its ball tip upwards, the sealing member is held down by the balancing member in a suitable position at the end of the ink column remote from the ball tip.

5. A writing instrument of the type specified, comprising aball writing end, a tubular element connected to the writing end, said element containing a suitable ink, a sealing member in said element at the end of the ink remote from the ball. forming a sliding t in the element. and

adapted; to. normally move along the element in contact with ink as the latterY is used. in: writing, said, sealing member having' a, bulk: density dif.- fering: from; thatv of' the ink, land' a balancing member independently movable in the; element and having such a hulk. densityg. that it cooperates with the: sealingy member; when necessary, to compensate, in any position of the writing instrument, any tendency ofthe sealing member to move throng-n said toward the writing point.

6. A reservoir writing instrument, according tov claim wherein the sealing' member in the reservoir forming a sliding nt therein has' a bull: density 'greater than that ofv the ink, and. the bal'- ancing, member is intermediate the sealingv mem;- ber and the writingv end' ofr the instrument disposed in the ink column, said balancing member having a bulk density less than that of the ink, the combination of the sealing member and the balancing member being such that when the instrument has its ball tip downwards the sealing member is held up by the balancing member in a suitable position at the end of the ink column remote from the ball tip, and when the instrument has its ball tip upwards, the sealing member is maintained separate from the balancingT member in a suitable position at the end of the inlr column remote from the ball tip.

7. Apparatus according to claim 6, wherein the sealing member has an annular rim at its rear face forming a sharp inner edge limiting the inward spread of the meniscus or" the ink contained in the reservoir.

8. Apparatus according to claim 6, wherein the radial spacing between said edge and the interior surface of the reservoir is less than 0.65 mm.

9. Apparatus according to claim 6, wherein the sealing member is in the form of a skirted piston and the edge is the inner edge of the piston skirt.

10. in a writing instrument of the ball point type, the improvement comprising a suitable ink containing reservoir of tubular internal form having an internal cross sectional area of not more than llo and not less than 5 sq. mm., a ball writing end in connection with the reservoir, a reservoir-sealing member having a bull: density not exceeding about 0.9 gr./cc. in the reservoir forming a sliding nt therein, said sealing member being adapted to iioat on the ink in the reservoir and being normalh7 remote from the ball writing end when said end is in writing position and a balancing member in the reservoir which is free to move in the ink in the reservoir, said balancing member having a bulk density between 7.9 gr./cc. to 11.4 gr./cc. and dinering from that of the sealing member, the construction and disposition of the parts being such that, when the reservoir is charged with a suitable inl: of a density intermediate the bulk densities of the sealing and balancing members, a meniscus is formed between the sealing member and the inner surface of the reservoir and the sealing member is maintained in stable eqilibrium at that end of the ink column remote from the ball in all attitudes of the instrument.

11. A reservoir writing instrument, according to claim 1G, having an oleaginous ink or" e viscosity of not less than poises at 37 C.

l2. A writing instrument of the ball point type comprising a ball writing end, a reservoir in connection with said end for containing a suitable writing ink, said reservoir having aperture means therein for communication with the atmosphere being; adapted to move in thev inle in said reser- Voir when the instrument is disposed in a. writ-h ing and. non-writing position.

A writing instrument of the ball point typecomprising a. writing end, a reservoir in con.-

nection. with. said end for containing a suitable writing intr,` and: having means,l for4 communica-- tion with the atmosphere, a, sealing member confon-ing with the shape of the reservoir and adapted to slide in said reservoir forming a sliding iit with the wall thereof, said member being adapted to float on the ink and being provided with a slrirted edge to prevent capillary creep of the ink over the sealing member, and a compensating balancing member in the reservoir approximating the diameter of the reservoir said balancing member being independently movable in the ins: in the reservoir, said balancing member being heavier than the ink in the reservoir, and adapted to move in the direction of the sealing member when the instrument is in an upright non-writing position, said sealing and balancing member forming a seal at the end of the ink column in the reservoir when the instrument is in a non-writing position.

la. A Writing instrument of the ball pen type comprising a ball point Writing end, a reservoir for containing a suitable ink therein connected at one end to said writing end, said reservoir having its other end in communication with the atmosphere, sealing means for the interior of the reservoir adapted to form a sliding t therewith and having a positive buoyancy with respect to the ink in the reservoir, and balancing means in the reservoir having external dimensions approximating the internal dimensions of the reservoir, adapted to slide in the reservoir, said last means being heavier than the ink in the reservoir and being adapted with the sealing means to form a seal at the end of the ink column in the reservoir when the instrument is in normal upright condition.

15. An apparatus for applying a iiuent material to an underlying surface, including a tubular body forming a fluent material reservoir and having at one end a writing tip, a follower piston having buoyant properties in relation to the fluent material freely slidable in the tubular body to follow the fluent material therein, and a weight in the tubular body movable by gravity therein independently of the follower piston, said weight adding its Weight to the follower piston to prevent iioating of the follower piston when the tubular body is turned to dispose the writing tip upwardly, and said Weight moving in the reverse direction to remove its Weight from the follower piston when the tubular body is turned to dispose the writing tip downwardly in operative position.

16. A writing instrument, according to claim 5, wherein the sealing member has a bull: density greater than that of the balancing member and wherein the balancing member is a bubble in the ink.

17. In a writing instrument of the ball point type, the improvement comprising a suitable ink containing reservoir of tubular internal form having an internal cross sectional area of not more than 40 and not less than 5 sq. mm., a ball writing end in connection with the reservoir, a reservoir-sealing member in the reservoir forming a sliding t therein, said sealing member being adapted to float on the ink in the reservoir and being normally remote from the ball Writing end when said end is in writing position and a balancing member in the reservoir which is free to move in the ink in the reservoir, said balancing member having a bulk density differing from that of the sealing member, the construction and disposition of the parts being such that, when the reservoir is charged with a suitable ink of a density intermediate the bulk densities of the 12 sealing and balancing members, a meniscus is formed between the sealing member and the inner surface of the reservoir and the sealing member is maintained in stable equilibrium at that end of the ink column remote from the ball in all attitudes of the instrument.

HANS REINHARD FEHLING.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,192,479 Nissen Mar. 5, 1940 2,194,348 Zoder Mar. 19, 1940 2,249,163 Nissen July 15, 1941 2,427,069 Randolph Sept. 9, 1947 2,438,786 Moore Mar. 30, 1948 

